Shape constancy in autism: the role of prior knowledge and perspective cues.

BACKGROUND Evidence suggests that individuals with autism may not attend to contextual information (conceptual or perceptual) when processing stimuli (Frith 1989; Shah & Frith, 1983). METHOD We investigated the role of prior knowledge and perspective cues when judging the shape of a slanted circle in individuals with and without autism. Individuals adjusted a shape on a computer screen to appear the same as a slanted circle. RESULTS Participants in all groups (autistic, moderate learning difficulties, children aged 9 years and adults) exaggerated circularity. Strikingly, however, individuals with autism were unique in exaggerating circularity significantly far less when perspective cues surrounding the slanted circle were eliminated. Prior knowledge that the shape was a slanted circle provoked a strong exaggeration effect in participants without autism, but not in those with autism. CONCLUSIONS Perhaps classifying the stimulus as a 'circle' was sufficient to provoke a strong exaggeration effect in those without (but not with) autism. In this domain, we show that perception in autism may be less influenced by prior knowledge, and therefore less 'top-down'.

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